This invention relates to an apparatus for conveying particles through a closed system wherein the conveying medium is a gas. More particularly, the invention relates to an apparatus for assuring that particles remain in suspension in a gaseous stream through a closed and elongated ducting system.
The task of conveying particle materials over distance via a gaseous medium, usually air, is complicated by the problem of the material settling out along the conveying system, which not only lowers the delivery efficiency but also tends to clog the conveying system and causes blockages to develop at various points along the system. For purposes of this discussion we will refer to the gaseous medium as being air, it being understood that any other convenient gaseous medium may be used in a particular conveying system. Delivery systems using the principle of pneumatic conveying attempt to solve the problem by developing an air flow velocity which is 3-4 times the terminal velocity of the particular particles being conveyed. Solving the problem using pneumatic conveying principles naturally requires an air volume flow source of considerable magnitude. This is especially true when particular applications are examined wherein the cross-sectional area of the conveying system may be equivalent to a pipe diameter of from 2 to 12 inches, and the conveying system may be several hundred feet in total length, and wherein the flow rate must be maintained throughout the entire length of the system.
A second approach to conveying particle materials is to utilize the principle of fluidized flow. This principle utilizes air turbulence to hold the particles in suspension; particles may be conveyed utilizing an air volume flow rate velocity of from 1/2 to 3 times the terminal velocity of the particular particles. Fluidized flow obviously requires a lesser capacity air blower with its attendant savings in energy consumption. In either conveying approach the particular volume flow rate is dependent upon factors such as the type of material being conveyed, the interior construction of the conveying path, the length of the total conveying system, the relative elevations of inlet and outlet, as well as the geometric configuration of the entire delivery system.
Fluidized conveying provides advantages in the efficiency of operation of the conveying system in terms of enabling relatively more material to be delivered at a given air flow rate. For example, under fluidized conveying principles a pound of air will typically convey twenty or more pounds of material, of course dependent upon the material characteristics. A pound of conveying air utilizing pneumatic conveying principles is usually limited to conveying less than twenty pounds of material. In addition, fluidized conveying offers advantages in better mixing or emulsion between the air and suspended particles, less wear on the interior parts of the conveying system, and lower degradation of materials by way of particle breakup along the delivery system.
Typical fluidizing systems are described in U.S. Pat. Nos. 2,806,636 and 2,795,464, owed by the same asignee as the present invention. The present invention is adaptable for use with systems of the type disclosed in these patents and its use therein will enhance the operation of the inventions described.